Examples of a conventional planar light source include: a light-emitting diode (hereinafter, abbreviated as LED) using a light guide plate; and an organic light-emitting diode (hereinafter, also referred to as organic electroluminescence element, organic EL element, or OLED).
Since around 2008, an LED light source using a light guide plate has rapidly come to be used not only for general lighting but also as, for example, a backlight for the main display (e.g., liquid crystal display: LCD) of a smart device (e.g., smartphone or tablet) that has become popular worldwide.
Such an LED light source is used not only as a backlight for main display but also as a backlight for common function key buttons provided in the lower part of a smart device.
There is a case where common function key buttons are provided with, for example, three kinds of marks representing “Home” (indicated by, for example, a square mark), “Return” (indicated by, for example, an arrow mark), and “Search” (indicated by, for example, a magnifying glass mark).
From the viewpoint of improving visibility, such common function key buttons are configured by previously forming dotted deflection patterns in a light guide plate according to the pattern shapes of the marks to be displayed and providing an LED light source on the lateral side of the light guide plate to emit light toward the side surface of the light guide plate. In such common function key buttons, light emitted from the LED light source enters from the side surface of the light guide plate, and is then totally reflected by the deflection reflecting surface of the deflection patterns toward the front surface of the light guide plate. As a result, light is emitted in predetermined patterns from the front side of the light guide plate, and therefore when the light guide plate is viewed from the front, the light patterns can be seen (see, for example, Patent Literature 1).
Further, for the purpose of improving the sensitivity of a sensor electrode of a capacitive information input unit using an LED light source to allow a sensor circuit to reliably detect a change in capacitance to stably process input operations by a user, a method is disclosed in which an adhesive layer having a higher permittivity than an air layer having the same shape is provided between a flexible printed circuit (hereinafter, abbreviated as FPC) having a sensor electrode formed thereon and a surface panel so as to be located in a position other than the position of an icon or the like to improve the detection accuracy of the sensor electrode that detects a capacitance (see, for example, Patent Literature 2).
On the other hand, there is also a move to use a surface-emitting organic electroluminescence panel (hereinafter, abbreviated as organic EL panel) to achieve lower power consumption and a more uniform luminance of emitted light. Such an organic EL panel is provided on the back side of a part of a cover glass where marks or the like are previously printed to display the marks or the like.
A smart device is absolutely required to have a tough function, and therefore a capacitive touch-sensing device for touch detection is usually provided on the back surface side of a cover glass in the display area and the common function key area of the smart device.
As such a touch-sensing device, a film/film-type touch sensor is often used which is obtained by laminating films enlarged to the same size as the cover glass. In the case of a smart device whose thickness is not particularly limited, a glass/glass-type touch-sensing device is sometimes used. As a touch-sensing system, a capacitive touch-sensing system is recently often used. For a main display, one of projected capacitive touch-sensing systems, called “mutual capacitive touch-sensing system”, is used which has fine electrode patterns in both x- and y-axis directions. This system allows so-called “multi-touch” so that two or more touches can be detected.
Since such a touch sensor is used, a light-emitting device having no touch function has heretofore been used in a common function key area. However, with the recent advent of so-called “in-cell”- or “on-cell”-type displays, a light-emitting device for common function keys has strongly been required to have its own touch-sensing function.
On the other hand, a common function key area does not need to have the above-described multi-touch function, and therefore one of capacitive touch-sensing systems capable of detecting On/Off, called “self-capacitive touch-sensing system”, can sufficiently fulfill functions required for common function keys. In the case of such a self-capacitive touch-sensing system, an electrode for touch detection has a simple pattern such as a solid pattern.
In the case of a surface-emitting organic EL panel, an anode, a cathode, or a protective metal foil layer constituting an organic EL element adversely affects the detection of a change in capacitance by the above-described capacitive touch-sensing system. For this reason, for example, an assembly needs to be provided on the light-emitting surface side of the organic EL element when a capacitive touch function is added to the organic EL panel. That is, such a significant restriction is placed on setting a touch function. Such a method in which an assembly is provided involves a need to additionally supply a touch device, and therefore has a problem of increase in economic burden.
In order to solve such a problem, a technique is known in which a capacitive sensing circuit is provided in an FPC used to mount an organic EL panel or an LED. However, in the case of an organic EL panel, an electrode plane constituting a capacitive sensing circuit is provided on the opposite side from the light-emitting surface of an organic EL element. As a result, an FPC is provided on the opposite side from the light-emitting surface. In this case, a structure illustrated in FIG. 8 that will be described later is obtained, but this structure has a problem that the touch-sensing accuracy of the FPC having the capacitive sensing circuit is very low.
On the other hand, in order to avoid the FPC from being provided on the back side of the organic EL panel, as illustrated in FIG. 9 that will be described later, the FPC may be provided outside the region of the organic EL panel. However, such a structure has a problem that an increase in the distance between the position where light is emitted and the position of the touch-sensing circuit or an increase in the total area of an organic EL module adversely affects the application of the organic EL module to a smart device required to have a small format.
Therefore, there has been a demand for development of an organic electroluminescence module (hereinafter, abbreviated as organic EL module) that is formed by compactly laminating an organic EL element as a light-emitting device and a wiring material to achieve a reduction in size and thickness, that has a high touch-sensing accuracy, and that is applicable to smart devices.